Global error pages with Jetty and grails

We wanted to configure global error pages for our grails app. Using your favorite search engine you quickly find the following info.

At the bottom it says that in order to support global error pages you have to forward to a context because error pages can only be handled within contexts/webapps.
So I started adding a context to the contexts dir which looked like this:

<Configure class="org.mortbay.jetty.webapp.WebAppContext">
      <Set name="contextPath">/</Set>
      <Set name="war"><SystemProperty name="jetty.home" default="."/>/webapps/mywebapp.war</Set>
      <Set name="extractWAR">false</Set>
...

This caused an “IllegalArgumentException: name” at startup. The solution was to set extractWAR to true. JSPs or other resources (like GSPs) cannot be used inside a war when extractWAR is set to false. But this way got another pitfall: using localhost:8080/mywebapp won’t work. So why not just forward all requests from / to /mywebapp. Said and done:

<Set name="handler">
  <New id="Handlers" class="org.mortbay.jetty.handler.RewriteHandler">
    <Set name="rewriteRequestURI">false</Set>
    <Set name="rewritePathInfo">false</Set>
    <Set name="originalPathAttribute">requestedPath</Set>
    <Call name="addRewriteRule"><Arg>/mywebapp/*</Arg><Arg></Arg></Call>
    <Call name="addRewriteRule"><Arg>/*</Arg><Arg>/mywebapp</Arg></Call>
    <Set name="handler">
here the old handlers are inserted...

Now /mywebapp points to my webapp. / gives a 500 and other invalid urls give a 404.
To use your custom error pages inside a grails app just add the error codes you want to map inside the UrlMappings.groovy file:

class UrlMappings {
  ...
  static mappings = {
    "500"(view:'/error')
    "404"(view:'/error404')
  }
}